The invention relates generally to ground-travelling machines and, more particularly, to an auto-center steering system for a steerable wheel of a ground-travelling machine which is operable to steer the wheel in alignment with a longitudinal axis of the machine.
Ground-travelling machines having steerable wheels are in common use. One type of such machines are ground-working machines for the creation of narrow ground trenches for a variety of purposes such as the laying of drainage tile, sewer lines, electrical lines, and similar applications. A common ground-working machine includes a four-wheeled tractor unit which supports at a rear end portion thereof an attachment, such as a trenching bar, that is pivotable about a transverse horizontal axis between an upwardly and rearwardly extended transport position and a downwardly and rearwardly extended trenching position. The mobility of the machines is substantially enhanced by providing that both the front and rear wheel or wheels of the tractor unit be independently steerable. The turning radius of the machine is decreased and the machine can be "crab-steered" when, for example, backfilling a trench that was previously dug. It is necessary to accurately return the wheels on-center, however, when the machine is transporting itself between projects or on the roadway. In such circumstances, it is important that the wheels be centered with respect to the machine so that they track accurately in the direction of travel.
Manual wheel or wheel steering systems are known wherein the wheel or wheels are returned to a roughly centered position by an operator who is guided by an indicator linked to a steering member of the steerable wheel or wheels. The mechanical systems are subject to inaccuracy in the centering of the wheel or wheels in that the linkage or other interconnecting device and indicator have a certain amount of hysteresis.